Electrical Discharge Machining - Wire Cut. Presented and Arranged by: Khairu bin Kamarudin

Transcription

1 Electrical Discharge Machining - Wire Cut Presented and Arranged by: Khairu bin Kamarudin

2 Introduction EDM Wire Cut Machining method primarily used for hard metals or those that would be impossible to machine with traditional techniques. EDM only works with materials that are electrically conductive with regardless of its hardness. (E.g: hastalloy, hard steel, titanium, inconel, carbide, ext;)

3 Introduction cont Used with computer numerical control (CNC), and machines frequently operate unattended. Workpiece typically is mounted on a table with two degrees of freedom. The movement of the table and wire are controlled by a computer that can compensate for overcut, wire thickness, and known errors in the workpiece.

4 Major Components Four major components. (1) Computerized Numerical Control (CNC) Think of this as The Brains. (2) Power Supply Provides energy to the spark. Think of this as The Muscle. (3) Mechanical Section Machine tool, worktable, taper unit, and wire drive mechanism. Think of this as The Body. (4) Dielectric System Water reservoir provides for filtration, and controls the condition and temperature of the water. Think of this as The Nourishment.

5 The Process Similar to contour cutting with a band saw, a slowly constant-moving wire travels along prescribed path acts as the cutting tool, cutting the work piece, with the discharge sparks acting like cutting teeth. Wire EDM machines utilize a very thin wire (.0008 to.012 in.) as an electrode. The wire is stretched between diamond guides and carbide that conduct current to the wire and cuts the part like a band saw. Material is removed by the erosion caused by a spark that moves horizontally with the wire.

6 The Process To cut plates as thick as 300mm (12 inches), and for making punches, molds, tools and dies from hard metals. It can also cut intricate components for the electronic industry. The Wire : usually made of brass, copper, tungsten or molybdenum; zinc or brass-coated and multi-coated wires diameter is typically about 0.30mm (0.012inch) for roughing cuts and 0.20mm (0.008inch) for finishing cut. high electrical conductivity and tensile strength. tension on the wire is typically 60% of its tensile strength

7 The Process- cont

8 The Process- cont Schematic illustration of the wire EDM process

9 The Process- cont When voltage conducts through the electrode, the deionized water is ionized. The resulting spark "melts the work piece. The amount of material removed is controlled within of one mm. Removing material by a series of rapidly recurring electric arcing discharges between an electrode (the cutting tool) and the work piece, in the presence of an energetic electric field. The EDM cutting tool is guided along the desired path very close to the work but it does not touch the piece. Consecutive sparks produce a series of micro-craters on the work piece and remove material along the cutting path by melting and vaporization.

10 Principles of EDM The particles are washed away by the continuously flushing dielectric fluid (deionized water). Once the machine starts, the wire is in continuous motion so that the cutting is actually being done by a new electrode all the time, thus solving the problem of electrode wear. The used wire is then discarded.

11 The Process- cont Work piece & the wire represent (+)ve & (-)ve terminal in a DC electric circuit. There is no physical contact between the wire and the part being machined The gap must always be filled with dielectric fluid

12 The Process- cont Cutting speed: generally given in terms of the cross-sectional area cut per unit time. The wire-cut uses water as its dielectric with the water's resistively and other electrical properties carefully controlled by filters and de-ionizer units. Function of dielectric : (1) Act as an insulator until the potential is sufficient high. (2) Provide a cooling medium to prevent heat buildup, and preventing thermal expansion of the part. (3) Act as a flushing medium and carry away the debris in the gap.

13 ADVANTAGES Complex geometry and intricate shapes can be cut easily. No cutting pressure or mechanical stresses imparted. No cutting forces generated; therefore, very fragile parts can be machined. Able to cut hard materials. No residual burrs on the workpiece. Can replace many types of contour grinding operations and eliminate secondary operations such as deburring and polishing. High accuracy and superior finishes.

14 DISADVANTAGES The operation of this machine cannot be stop instantly when it getting started because it s working continuously. Higher cost for manufacturing and cutting tool. Cannot cut a non-conductive materials. Workpiece size is limit for some machine. Temperature for wire cut must be maximum before cutting. Wire cut cannot be recycle.

15 PARAMETERS Spark generation:- Related to electrical current. Dielectric fluids between the spark The degree of contamination in the dielectric fluids will influence erosion rate of the workpiece which is with the increase of contamination degree, the erosion rate will decrease.

16 PARAMETERS cont Electrode (a) chemical properties and physical of electrode. (b) electrode dimensions. (c) electrode kinematics. (d) electrode from good electrical conductivity will resulted to high erosion rate. Workpiece Erosion rate of the workpiece - influenced by the chemical and physical properties of workpiece materials.

17 PARAMETERS cont Tolerance Similar to many other machines, EDM also has its error factors. So, it needs some tolerances for the final machined product. The essential error factors are as following: (a) error at final machined shapes due to error and erosion rate of electrode. (b) error due to machine set-up. (c) error in materials selection. (d) error by tool work gap.

18 PICTURE AND VIDEO EDM WIRECUT PRODUCTS VIDEO 1

19 THANK YOU FOR YOUR ATTENTION 19